Deism is without theism, that doesn’t make it atheism. The article is quite clear. Being a position of belief is indicated by the ism. The part before it defines the position of belief. Whether disbelief/lack of belief of the gods, or belief in no gods. It is not being without the belief of the belief in gods.

Now please clearly explain the difference between the position “no belief in gods” and “no belief in gods because the concept doesn’t yet exist”. That’s what your entire position hinges on, and you haven’t given any arguments for it.

Also, the article is quite clear in not supporting your position. It says:

-ism (/-ˌɪzəm/) is a suffix in many English words, originally derived from the Ancient Greek suffix -ισμός (-ismós), and reached English through the Latin -ismus, and the French -isme.[1] It means “taking side with” or “imitation of”, and is often used to describe philosophies, theories, religions, social movements, artistic movements, lifestyles,[2] and behaviors.[3] It is typically added to nouns.

No mention of requirements regarding pre-existing concepts or anything similar.